Build sagelib from build/pkgs/sagelib/src, fix `setup.py sdist`, add spkg-src and tox.ini

[mkoeppe]

As a follow-up to #29411, we set up a separate directory build/pkgs/sagelib/src with symlinks into SAGE_ROOT/src so that sagelib's setup.py does not have access to the whole tree SAGE_ROOT/src.

We fix setup.py sdist, which can be tested using spkg-src (which builds a pip-installable tarball in upstream/) and tox:

./sage -sh -c '(cd build/pkgs/sagelib/src && tox -v -v)'
./sage -sh -c 'build/pkgs/sagelib/src/.tox/python/bin/sage-ipython'

The call of ./sage -sh is necessary so that SAGE_LOCAL is set.
Moreover, for scripts that use sage-env, also SAGE_ENV_SOURCED is crucial for the correct operation; otherwise sage-env sets things based on SAGE_LOCAL again.

Depends on #29701

CC: @kiwifb @jhpalmieri @dimpase @kliem @isuruf @vbraun

Component: refactoring

Author: Matthias Koeppe

Branch/Commit: ccc67b0

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29950

[mkoeppe]

Branch: u/mkoeppe/build_sagelib_using_installed_sage_setup

[sagetrac-git]

Commit: 1ab75a9

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

0459006	.gitignore: Ignore generated files in build/pkgs/*/src
1ab75a9	Build sagelib using the installed sage_setup

[mkoeppe]

Work Issues: add spkg-src

[mkoeppe]

Author: Matthias Koeppe

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

3d83c12	build/pkgs/sagelib/spkg-src: New
a2bde50	src/MANIFEST.in: prune .tox
4b258d3	src/MANIFEST.in: Remove bitrotted file
a29cd2d	build/pkgs/sagelib/MANIFEST.in: New

[sagetrac-git]

Changed commit from 1ab75a9 to a29cd2d

[mkoeppe]

Changed work issues from add spkg-src to Fixup MANIFEST.in

[mkoeppe]

comment:8

sdist is broken: Files named ** end up in the tar file.

[mkoeppe]

Changed dependencies from #29411, #29847 to #29411, #29847, #29701

[mkoeppe]

comment:10

sagemath/cypari2#93

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. Last 10 new commits:

7f8850a	src/module_list.py: Document that it is obsolete
26a85a4	Merge branch 't/29702/move_all_code_from_src_setup_py__src_fpickle_setup_py_to_sage_setup' into t/29701/replace_use_of_module_list_optionalextension
5d5803e	src/sage/graphs/planarity.pyx: Add forgotten distutils directive
a0be9b6	Merge branch 't/29790/move_extension_options_from_src_module_list_py_to__distutils___directives_in_the_individual_files__part_5__sage_graphs_' into t/29701/replace_use_of_module_list_optionalextension
14396af	Merge tag '9.2.beta2' into t/29701/replace_use_of_module_list_optionalextension
821e337	Merge branch 't/29701/replace_use_of_module_list_optionalextension' into t/29950/build_sagelib_using_installed_sage_setup
eeb6ba4	build/pkgs/sagelib/src/requirements.txt, tox.ini: New
ce8b84d	build/pkgs/sagelib/src/MANIFEST.in: Prune sage/ext/interpreters
a9a1335	build/pkgs/sagelib/src/requirements.txt: Add packages required for runtime
c3b8f8f	Suggest tox -v -v

[sagetrac-git]

Changed commit from a29cd2d to c3b8f8f

[mkoeppe]

Description changed:

--- 
+++ 
@@ -1,2 +1,8 @@
-After #29411 and #29847, we set up a separate directory `build/pkgs/sagelib/src` with symlinks into `SAGE_ROOT/src` so that sagelib's `setup.py` does not have access to the whole tree `SAGE_ROOT/src`. In particular, we arrange for the installed `sage_setup` (#29847), rather than the one from the source tree, to be used.
+As a follow-up to #29411, we set up a separate directory `build/pkgs/sagelib/src` with symlinks into `SAGE_ROOT/src` so that sagelib's `setup.py` does not have access to the whole tree `SAGE_ROOT/src`.
 
+We fix `setup.py sdist`, which can be tested using `spkg-src` and `tox`.
+
+```
+./sage -sh -c '(cd build/pkgs/sagelib/src && tox -v -v)'
+```
+

[mkoeppe]

Changed work issues from Fixup MANIFEST.in to Rebase away from #29847